Lighting unit



Jan. 1e, 19345A n. A. s. PAGET 1,943,877'v y I LIGHTING UNIT originalFi1ed'Jan.,4,'1929 4 Smets-sheet' 1 R. A. S.- PAGET Jan. 16, 1934.

LIGHTING UNIT Original Filed Jan. 4, 1929 4 Sheets-Sheet 2 AJan. 16,1934. R. A. s. PAGET 1,943,877

LIGHTING- UNIT original Filed Jan. 4, 1929. 4 sheets-sheet 3 Jan. 16,1934. l R A, s, PAGE-r LIGHTING UNIT 4 sheets-Sheet '4 Original FiledJan. 4, 1929 Patented jan. i6, 1936i 1,943,877 LIGHTING UNIT RichardArthur Surtees Paget, Lancaster Gate; England, assignor to ThermalSyndicate Limited, Neptune Bank; Wallsend-on-Tyne, England l ApplicationJanuary 4, 1929, serial No. 330,318. and in Great Britain January 7,1928. Renewed June 14, 1933 4 Claims. (Cl. 24o- 4.1)

coloured globes or to use the light from a lament lamp only afterreflection from coloured surfaces. Colour screening or colour reflectingdevices are not desirable, however, owing to the' resultant reductionofthe lighting efficiency of the filament lamps. It has also beensuggested to provide a composite lighting unitconsisting of a quartzmercury arc lamp and filament lampo arranged so that the chemicallyactive ultraviolet rays of the quartz lamp may be combined with theultra-red radiations from the lament lamps, the reason for the additionof the filament lamps, being to improve the colour` of the radiationfrom the mercury lamp. No explanation however has been given as to theextent of this addition or of the colour quality desired. Moreover,Where such a lighting unit is used as a general illuminant, it has notbeen proposed to provide protection from the injurious short 'wavelength radiations from the mercury arc, and with the unscreened mercuryarc, dangerous sunburnin'g would occur if the unit were used as an'ordinary source of illumination.

According to the present invention I provide a high efficiency lightingunit, approximating to daylight both as to its visible and ultra violetcontent, by combining Within a casing,1lamps of different character,Whose radiations are complementary in relation to wave length for exsample mercury vapour lamps or other lamps producing ultra violet raysand metal filament lamps, ,the combined radiations being transmitted bya layer of translucent fused quartz or the equivalent, so proportionedas to-thickness and texture as to transmit only the radiations required.The quantity of illumination to be used from each source is determinedso that the resulting visible radiation is brought as close as possibleto' the quality which exists in ordinary daylight. I further specify thematerials and methods which are required to produce this illuminationtogether with a safe land tolerable amount of ultraviolet radiation.`

Because of the Way in which the mercury lamp emits its radiation, thatis to say, discontinuously, so far as` the spectrum is concerned, acomplete match With ordinary daylight is not possible by the addition offilament lamps but thel composite radiation which I produce by themethod hereinafter described is not further removed from daylight valueson the blue side .than is the v filament illumination removed on the redside.

The features which I have found require experimental investigation inmaking a lighting unit to fulfill the required conditions are:

1st. The ratio of filament and mercury arc illumination. 2nd.Theensuring of a uniformly illuminated bowl surface. 3rd. Properventilation, and 4th. Control of the amount of ultra violet radiationsent out by the lamp.

Taking these features in turn, it is desirable to use the maximum amountof mercury arc illumination permissible in order to increase thelighting efficiency of the unit as much as possible, since, as is Wellknown, the mercury arc lamp has a higher luminous efficiency thanordinary filament "w lumens per watt with the radiation from one directcurrent mercury vapour arc contained in a quartz tube 6 inches long and15 millimetres external diameter consuming 400 watts together with itsseries resistance and operating at an overall eiiiciency of about 15lumens per watt, a very 4fair approximation to the quality of ordinarydaylight is obtained. In this case an equal Wattage is supplied to bothsystems. These figures are given only by way of example and I do notlimit myself to these specific amounts of filament and mercury arcillumination. Smaller or larger units may be prepared retaining aboutthe same ratio of filament to mercury arc illumination. The proportionof illumination from'themercury arc may be increased so that a greaterproportion up to a maximum of twice the amount indicated of mercury arcillumination is used, still producing a lamp which functions under therequired conditions, although the precise ratio specified gives the bestmatch to daylight. I have given the power consumption of the mercuryvapour lamp with reference to a direct current burner running at aspecified efficiency but no restriction is to be placed on the type ofburner whether alternating or direct current, provided that it operatessubstantially in the range Where itsl efficiency is between 15 to 30lumens per watt. With more efficient mercury vapour lamps the powerconsumption required for this part of the unit-is to be reduced pro ratafor its increase in eiciency above 15 lumens per watt so that thedesired ratio of filament and mercury arc illumination is kept in theproportions already set out. Similarly for filament lamps of greater orless efficiency than 11 lumens per watt. y

In order to limit the amount of ultra-violet radiation the assembledlamps are enclosed by a screening and diffusing bowl of translucentfused silica or quartz or other suitablematerial which will transmit theultra violet rays of the desired wave length and to produce uniformillumination on the surface of the enclosing bowl I find it l best toarrange the various units symmetrically with reference to the axis ofthe bowl.

To maintain `this uniform illumination with `lamps of diilerentbrilliancy and colour values careful spacing of the various lamps awayfrom the surface of the screening bowl is required. At the same time tosafeguard the user, provision must be made that no radiation from themercury lamps reaches the working plane unless after passing through.the obscuring bowl or after reflection.

In the accompanying drawings I have shewn examples of preferredconstructions of lamp units in accordance with the invention. Figure 1shews an elevation in part section lof aunit designed for use with theresistance of the mercury lamp unit similar' to that shewn in Figure l,but arranged to accommodate the ballasting resistance for the mercuryvapour lampl in the upper part of the housing; Figure 4 is similar toFigure l, but adapted for use with a mercury vapour lamp of theatmospheric type where no tilting arrangement is required to start thearc; Figures 5 and 6 give a general View in elevation of a unit similarto that shewn in Figure 1 and illustrating in Figure 6 how the lowerbowl may be opened on its hinge for cleaning purposes; Figures '7 and 8shew a similar unit to that shewn in Figures 5 and 6; Figures 9 and 10shew in elevation and plan a lighting unit in which a mercury vapourlamp surrounds a filament lamp.

Referring to Figures 1 and 2 the construction shews a straight arc tubelamp l, around which are symmetrically arranged .four lament lamps 2, inthe diametral plane of the approximately hemispherical silica bowl 3,which serves to enclose the lamps. Additionally, reflectors 4, may beadded disposed at an angle to the axis of the arc tube to distribute theradiation from the mer-- cury arc into those portions of the bowl 3, notwell illuminated by it, particularly those portions lying near to theelectrode chambers 5 and 6 of the arco Similar reflectors may be usedsuitably arranged to throw the rays from the filament lamps on to thatpart of the bowl which would otherwise be in shadow such shadow beingcaused by another detail of the assembly.

Double metal rings 7 and 8 carry the upper silica bowl 9 and the lowersilica bowl 3, the inner ring 7 being hinged to the outer ring 8 to giveeasy access to the lower bowl for cleaning purposes, as shewn in Figures5 and 6.

The arc tube shewn is of the vacuum type and is provided with the usualtilting mechanism.

-When the unit is in operation air currents pass in through holesv 11,drilled in the double rings 7 and 8, and out at the top 'through thealuminium cover 12.

.the mercury vapour lamp 1.

In Figure 3 supports'l`3 carry the metal hood 14 and also the platform15, to which is'xed the tilting arrangement 16 to start the mercuryvapour lamp 1. A cylinder '17 of insulating material is provided and onthis is wound the ballasting resistance wire which is connected inseries with The resistance wire when heated induces a circulation ofcooling air within thecasing. The unit is otherwise similarto that shewnin Figures 1 and 2. In operation air vcurrents pass in through holes l1and through the annular space between the platform 15 and the hood 14,and out at the top as shewn by the arrows.

Figure 4, as hereinbefore mentioned, shews a similar unit to that ofFigure 1, except that a mercury vapour lamp 1a, of the atmospheric typeis provided.

Figures 7 and 8 shew a similar unit to that shewn in Figures 5 and 6 butin this case the lower Vbowl 3, and its supporting ring 18, is suspendedfrom the main structure by means of three or more chains or cords 19,which pass over pulleys 20. Balance weights 21, are attached to theother ends of these chains orcords. Figure 7 shews the lower bowl in theclosed position and Figure 8 shews this bowl lowered for cleaning.

A handle 22, may be attached to the bottom of the bowl 3, as aconvenient means for raising or lowering the bowl.

Figures 9 and 10 shew in elevation and plan, a lighting unit having amercury vapour lamp with its lighting tube 23 arranged in the form of acircle or ring inside which -is placed the filament lamp 24.

In this unit the arrangement with regard to the opening of the lighttransmitting surfaces or bowls 9 and 3, may be similar to those shewn inthe preceding Figures 5, 6, 7 or 8 and can be arranged to suit anyparticular requirements. In all cases the inside of the bowls should beeasily accessible for cleaning purposes: this is important in view ofthe fact that a small amount of dust accumulation will cut off theultra-violet radiation.

With the types of enclosing housings which are commonly available whenused only with filament lamps the problem of ventilation is not seriousand the cooling of these units is principally ac' complished by thermalradiation and convection from the outer fittings and not by an internalcirculation of air. I have found that composite units of the typereferred to in this specification require careful arrangement so that nointerference occurs with the operation of the mercury arc lamp andv alsoso that injury may not be done to the filament lamps at or about those portions where joints are made with metal caps and the like, and indeedalso injury directly to the glasses used in this type of lamp, byoverheating. To escape such injuryto the filament lamp or lamps andfurther to maintain the mercury lamp in stable operation at its desiredrating I arrange the various components of the unit symmetrically asalready specified and assist the natural ventilation of the lamps sothat cold incoming air may be directed on to the mercury lamp and-alsoon to those points of the filament lamp or lamps which require specialcooling.

Because of the use of quartz mercury arc lamps in the assembly of thelighting units it is necessary to use a suitable enclosing bowl or fitting which shall cut down the intensity of ultraviolet radiation in theworking plane to a safe limit, and properly diuse and intermingle thelight from the various sources which it encloses.

I have found however as the result of experivments that the mostsuitable material for this purpose is translucent fused silica orquartz, of the general type obtained by fusing pure quartz sand 4and ina thickness between lg and 1/8 of an inch.

lamp so that at common working distances onlyv, a'mild sun-burningeffect is obtained upon pro- 20:

tracted exposure. It is generally considered that radiations of a waveIlength less than 2500 A'. U.

have injurious effects on human tissues and the exclusion of theseradiations which are emitted by the mercury vapour lamp is an importantadvantage depending upon the use of the translucent silica bowl. It ispossible further by altering the texture (that is to say, the size andnumber of air' bubbles in the silica) and increasing or diminishing thethickness of section of bowl used to control the output of ultra-violetradiation from the lamp over a considerable range without interferingmuch with the transmission of visible radiation. As an example of thecontrol of the bowl upon the output of ultra-violet radiation, with aunit composed of four 100 watt lament lamps 'together with one mercurylampconsuming over all 400 watts in a silica bowl of the type indicatedand about T16" thick, exposure at two feet from the assembled unit fortwo hours produces a sun-burn effect equivalent to that got by exposureto the naked lamp at the same distance for about vthree minutes. Sunburnof this type would be produced by the normal medical dosage of aboutthree minutes and is commonly known as the rst stage of erythema. Atgreater distances from a unit of the type indicated the intensity ofultra violet radiation falls off much in the same manner as the ordinaryvisible i1- lumination so that at ordinary working distances say 6 feet,the time of exposure. required for'sunburning is of the order 30 hoursor more. Such exposure is quite safe for continuous daily use of theunit as an ordinary source of illumination, and because of the presenceof ultra-violet radiation important benefits to the health and wellbeing of the user are to be expected.

I have found, as a result of photo-electrical measurements that byaltering the texture of the silica bowl, by partly re-fusing or glazingitin an electric arc, the transmission .of ultra-violet radiation isvery much increased without interferingsensibly with its transmission ofordinary visible illumination. The extent of this increase may be asmuch as eight times when the bowl is glazed from each of 4its surfaces.Thus, by adjusting the extent of this glazing treatment, and/or alteringthe thickness of the bowl, the transmission of ultra-violet radiationcan be accurately controlled, as also the mechanical strength. L

It will thus be seen that when I use a fused silica or quartz bowl Icanl control the trans- When the minimum amount of ultra violet rays isrequired I would use a thick unglazed bowl whilst for the maximum amountof ultra violet rays a thin bowl glazed on both sides would be used andfor intermediate strength I have the alternatives such as a thinunglazed bowl or a slightly thicker bowl glazed on one side only. Whenmechanical strength is of some consideration I prefer to use a fairlythick bowl glazed or not as circumstances require.

I have found, further, as a result of tests that no injurious effectsare produced upon the human eye by irregular reflection of ultra-violetradiation from common working surfaces when lamps of this type areused'as a general source ofvillumination. y

Where it is required completely to enclose the lamp which isadvantageous to prevent deposition of dust on the transmitting surfacesthe up-` per cover of the bowl may be partly of translucent fused silicaand partly of metal but the use of fused silica is not essential for Ihave found, that very little ultra-violet radiation is reflected bythematerials ordinarily used toproduce a white ceiling in a room. In caseswhen the lamps are intended to be used in a dusty atmosphere as forinstance in a factory or warehouse, it would be advisable to makearrangements to prevent as far as possible any dust entering andsettling on the inside of the bowls. This can be done by covering allVentilating holes and the chimney with fine wire gauze. This gauze willalso prevent house flies and other .winged insects from entering thelamp and collecting in the bottom of the bowl.

In my description I have exemplified only the use of direct currentmercury lamps which have the important advantage of easy starting, but Ido not wish to confine myself to this type of bm'ner and nothing in mydescription is altered in sense if, for mercury vapour lamp eitherdirect or alternating current mercury vapour lamp is read. The lamp maybe most simply arranged for distant control by incorporating a'suitablerelay with a solenoid, and plunger in mechanical connection with themercury lamp, so that upon closing the circuit to the lamp, the lamp istilted continuously until the arc strikes and then this mechanism isrendered inoperative by' the relay.

Aall in the mercury lamp and its resistance, and

400 watts in the filament lamps, the efficiency of the unit in lumensper watts is 4.6, whereas the efficiency of filament lamps only,arranged in a similar partly enclosed diffusing bowl' is only 3.9

lumens per watt, a gain of 8 per cent. It is further preferable in theseunits to use a mercury lamp of as large a size as is permissible sincethese are' more efficient, thus by way of example withA a mercury lampconsuming over all 417 watts 65 per cent of the total power is used inthe lamp proper, Whereas with a lamp which consumes over all 218 wattsthe percentage of power consumed by the lamp is only 42 lper cent.

In my description of the lamp 'I have referred only to the combinationof a quartz mercury va.- pour lamp and lament lamps but I do not limitthe scope of this invention to such a combination;

5 I may use other forms of lamps giving the required amount of ultraviolet rays which when used in combination with filament lamps securevapproximately the same complementary series of radiations with a surplusof short Wave component requiring selective ltering.

What I claim is:

1. A lighting unit comprising a source of ultraviolet radiation and ascreen of fused silica, the.

arc arranged so that the heat generated in the resistance induces acirculation of cooling air within said screen.

3. A lighting unit as dened in claim 2, in which there is also afilament lamp within the screen.

4. A lighting unit which comprises a plurality of complementary lightsources which together give a spectrum extending over the range ofdaylight, including the ultra violet, the light sources being soselected and proportioned in intensity as mutually to compensate fortheir respective deilciencies in spectral range, and means substantiallyenclosing said light sources comprising a screen of translucent silica,having bubbles, glaze and thickness regulated to absorb a relativelyvery large proportion of the radiation in the objectionable far ultraviolet part of the spectrum and to transmit a relatively largeproportion of the beneficial near ultra violet part of the spectrum.

RICHARD ARTHUR SURTEES PAGET.

